This invention relates to molded articles and to processes for their fabrication.
Thermoforming is utilized for making articles from sheets of thermoplastic resins, for example, acrylics (acrylonitrile polymers), polycarbonates, polyesters, polyimides, polypropylene, polystyrene and polyvinyl alcohol. One of the disadvantages of the process is that, using thermoplastic resins, it is not always possible to obtain the strength properties desired. As an example, thermoforming has been attempted for bodies of certain airborne objects. However it was found that such bodies readily cracked on landing. In order to increase the strength properties of these airborne objects it has been attempted to thermoform a thermoplastic body and then, using the same mold, spray up or lay up a thermoset body. The two molded articles were then to be bonded together to form a two ply airborne article. It was found however, that this method was unsatisfactory. It was not only difficult to get perfect fit with all surfaces of one body in contact with all bonding surfaces of the other, but an adhesive could not be found which bonded the thermoplastic piece to the thermoset counterpart. This is particularly true if the thermoset plastic is a cured epoxide resin. It is most difficult to bond an epoxide resin to a thermoplastic resin.
In view of this bonding problem it was decided to layup a fiber-reinforced epoxy resin on the previously thermoformed thermoplastic article to increase its strength properties. This process also proved to be unsatisfactory. The cured epoxy impregnated fiber cloth did not adhere to the thermoplastic article. However in accordance with this invention a process is provided wherein a fiber-reinforced epoxy resin layer is bonded to a mating thermoplastic resin layer.